We present an approach called object behavior specification that combines principles of systems theory with those of object orientation. The approach adds a middle layer between the set-theoretic formalism of DEVS (discrete event system specification) and its implementation in C++ and JAVA. Historically, the implementation came first and the object behavior specification was abstracted from it. However, once established, the approach may enable enhanced reuse of DEVS implementation designs. We also show the applicability of the approach to improved formalization of animation and dynamic structure implementations.